The present invention relates to communications apparatus such as a portable telephone set and a PHS (Personal Handyphone System) which is equipped with a first and a second antenna and performs communications via antenna switchover, and in particular, to communications apparatus which uses fewer signals to suppress a decrease in the transmission power and degradation in the receiving sensitivity.
Conventionally, communications apparatus to perform diversity reception for base stations and mobile stations is equipped with a plurality of antennas and selects an antenna which shows the highest signal level among those received by the plurality of antennas in order to perform reception by using the antenna, so that degradation in the receiving sensitivity caused by fading during travelling can be suppressed.
An example of the related art is shown in FIG. 5. FIG. 5 is a configuration diagram showing the conventional communications apparatus. In FIG. 5, the communications apparatus according to the related art is communications apparatus such as a PHS for performing communications via the TDMA (Time Division Multiple Access) system. The communications apparatus in FIG. 5 is composed of a transmitter 11, a receiver 13, a transmission/reception selector switch 15 for switching to the transmitter 11 or the receiver 13, antennas 17a and 17b, an antenna selector switch 19 for switching over the antennas 17a and 17b, and a controller 21 which generates a control signal C11 for controlling the transmission/reception selector switch 15 and supplies the control signal C11 to the transmission/reception selector switch 15 as well as generates a control signal C12 for controlling the antenna selector switch 19 and supplies the control signal C12 to the antenna selector switch 19.
The control signal C11 is composed of a transmission selecting signal C11a for switching to the transmitter 11 and a reception selecting signal C11b for switching to the receiver 13. The control signal C12 is composed of an antenna selecting signal C12a for switching to the antenna 17a and an antenna selecting signal C12b for switching to the antenna 17b. 
The transmission/reception selector switch 15 switches to the transmitter 11 when the transmission selecting signal C11a is high and the reception selecting signal is low, and switches to the receiver 13 when the transmission selecting signal C11a is low and the reception selecting signal C11b is high. Meanwhile, the antenna selector switch 19 switches to the antenna 17a when the antenna selecting signal C12a is high and the antenna selecting signal C12b is low, and switches to the antenna 17b when the antenna selecting signal C12a is low and the antenna selecting signal C12b is high.
In the conventional communication apparatus, an antenna which received a signal having a higher signal level is identified by comparing signal levels of receive signals received via the antenna 17a and the antenna 17b, and uses the identified antenna which received a signal having a higher signal level to perform reception.
For example, as shown in FIG. 6, when transmission is performed at a transmitting slot T1 by using the antenna 17a, the transmission selecting signal C11a is driven high and the reception selecting signal C11b is driven low, the antenna selecting signal C12a is driven high, and the antenna selecting signal C12b is driven low. Meanwhile, when reception is performed at a receiving slot R1 by using the antenna 17b, the transmission selecting signal C11a is driven low and the reception selecting signal C11b is driven high, the antenna selecting signal C12a is driven low, and the antenna selecting signal C12b is driven high.
However, the conventional communications apparatus is equipped with a transmission/reception selector switch 15 and an antenna selector switch 19 serially connected between the transmitter 11 or receiver 13 and the antenna 17a or 17b. Thus transmission signals or reception signals pass through these two switches. Accordingly, transmission signals or reception signals suffer from a signal level loss each time they pass through the switches, thus generating a decrease in the transmission power and degradation in the receiving sensitivity corresponding to the two switches.
The conventional communications apparatus is equipped with separate switches for transmission/reception switching and antenna switching respectively, thus requiring individual control signals C11 and C13. That is, in conventional apparatus in FIG. 5, the control signal C11 for controlling the transmission/reception selector switch 15 is composed of a transmission selecting signal C11a and a reception selecting signal C11b, and the control signal C12 for controlling the anntenna selector switch 19 is composed of an antenna selecting signal C12a and an antenna selecting signal C12b, thus requiring control via four control signals.
The invention is proposed in view of the conventional problems and aims at providing communications apparatus which suppresses a decrease in the transmission power and degradation in the receiving sensitivity via fewer control signals.
In order to solve the foregoing problems, communication apparatus according to the first aspect of the invention comprises a first antenna, a second antenna, a controller for generating first and second control signals based on the transmission or reception instruction and selection instruction from the first or second antenna, a transmitter switch for switching transmission signals to either the first or second antenna via connection switchover depending on the first and second control signals, and a receiver switch for receiving signals from either the first or second antenna via connection switchover depending on the first and second control signals, wherein the second antenna is connected via the receiver switch when the first antenna is connected via the transmitter switch and that the first antenna is connected via the receiver switch when the second antenna is connected via the transmitter switch.
Communication apparatus according to the second aspect of the invention comprises a first antenna, a second antenna, a transmitter, a receiver, a controller for generating a first control signal which is enabled when the first antenna is selected in transmission and a second control signal which is enabled when the second antenna is selected or generating a first control signal which is enabled when the second antenna is selected in reception and a second control signal which is enabled when the first antenna is selected, a first transmitter switch which is connected between the first antenna and the transmitter and is turned on/off based on the first control signal, a second transmitter switch which is connected between the second antenna and the transmitter and is turned on/off based on the second control signal, a first receiver switch which is connected between the first antenna and the receiver and is turned on/off based on the second control signal, and a second receiver switch which is connected between the second antenna and the receiver and is turned on/off based on the first control signal.
Communication apparatus according to the third aspect of the invention is communications apparatus according to the first aspect or second aspect of the invention, wherein the controller generates either the first control signal or the second control signal and that the other second control signal or first control signal is generated via signal inversion of the first control signal or the second control signal.
Communications apparatus according to the fourth aspect of the invention is communications apparatus according to either of the first, second or third aspect of the invention, wherein the apparatus comprises detecting means for detecting the signal level or signal field strength of the transmission signals or reception signals and that the controller makes an instruction of selecting the first or second antenna based on the detection results of the detecting means.
Communications apparatus according to the fifth aspect of the invention is communications apparatus according to either of the first, second, third or fourth aspect of the invention, wherein the apparatus performs the transmission or reception via the Time Division Multiple Access (TDMA) system.
In communications apparatus according to the invention, when the controller generates the first and second control signals based on an instruction of transmission or reception and an instruction of selecting the first or second antenna, transmission signals are connected to either the first or second antenna in the transmitter switch and signals are received from either the first or second antenna in the receiver switch, via connection switchover depending on the first and second control signals. When the first antenna is connected in the transmitter switch, the second antenna is connected in the receiver switch. When the second antenna is connected in the transmitter switch, the first antenna is connected in the receiver switch.
Thus, in transmission, transmission signals are output from the transmitter are supplied to either the first or second antenna via the transmitter switch, while in reception, receive signals are received from either the first or second antenna via the receiver switch. In conventional apparatus, a transmission/reception selector switch and an antenna selector switch are serially connected between the first or second antenna and a transmitter or receiver, thus generating a signal loss corresponding to two switches. According to the invention, a transmitter switch or receiver switch is respectively connected between the first and second antennas and the transmitter or receiver, thus generating a signal loss corresponding to a single switch on the transmission signals or reception signals. This can reduce a signal level loss in the switch and suppress a decrease in the transmission power or degradation in the receiving sensitivity, thus reducing the error rate of signals.
Especially, in the communications apparatus according to the second aspect of the invention, when the first antenna is selected in transmission, the first transmitter switch and the second receiver switch are turned on via the first control signal so that the output of the transmitter is connected to the first antenna and the second antenna is connected to the receiver. The same connection state is attained when the second antenna is selected in reception. Meanwhile, when the second antenna is selected in transmission, the second transmitter switch and the first receiver switch are turned on so that the output of the transmitter is connected to the second antenna and the first antenna is connected to the receiver. The same connection state is attained when the first antenna is selected in reception.
Conventional communications apparatus comprised independent switches for transmission/reception switchover and antenna switchover and generates control signals for respective switches via independent logic. Communications apparatus according to the invention generates control signals via complex logic composed of transmission/reception switchover and antenna switchover conditions to let the transmitter switch or receiver switch operate correspondingly. This reduces the number of control signals and is advantageous in circuit integration or apparatus downsizing from the viewpoint of the wiring and the number of output ports of the controller.
Especially, in communications apparatus according to the third aspect of the invention, the controller generates either a first control signal or a second control signal and generates the other signal by inverting the other signal via the inverter (NOT gate), etc. This reduces the number of control signals to half that in communications apparatus according to the second aspect of the invention.
Especially, in communications apparatus according to the fourth aspect of the invention, the detecting means preferably detects the signal level or signal field strength of the transmission signals or reception signals and the controller preferably makes an instruction of selecting the first or second antenna based on the detection results of the detecting means, and in communications apparatus according to the fifth aspect of the invention, transmission or reception is preferably performed via the TDMA (Time Division Multiple Access) system.
For example, in the antenna-switched diversity reception, antenna switchover is made based on information internal to the apparatus such as C/N (carrier to noise ratio), signal level (for a system where noise power is specified by the internal noise), or signal field strength. In case the reception system path is identical with the transmission system path, diversity reception is allowed where reception level prior to transmission is detected for each antenna and an antenna showing the higher reception level is selected. Further, in communications via the Time Division Multiple Access (TDMA) system, transmission or reception is made at a different timing (slot) on the time axis; antenna switchover based on the internal information such as C/N, signal level, and signal field strength before starting the transmitting/receiving slot can reduce noise which accompanies antenna switchover.